1. Technical Field of the Invention
The present invention relates generally to a top load seal protection feature. More particularly, the present invention relates to a load bearing thread which transmits stacking load from the top wall of a closure to the threads of a container in order to prevent seal failure under stacking load conditions.
2. Description of the Related Art
When manufacturers mass-produce containers and closures containing food, drink, and the like, the containers are usually shipped to distributors and vendors for public consumption. In order to prepare the containers for shipping, the containers are often stacked in a vertical manner and placed in boxes or crates in a space saving configuration. Throughout shipping and storage of the containers, they remain in this vertical configuration for various periods of time. The extended storage times often result in large vertical loads being placed on the container closures, which may not be factored into their design. As a result of the stacking, large loads may cause sealing gaskets located within the closures to rupture in turn causing leakage, spoilage, or destruction of the food product.
Current container closure designs generally suffer from an array of disadvantages, such as those described above, which detract from their efficiency and use. For example, U.S. Pat. No. 4,512,493 to Von Holdt discloses a molded bucket having high stack strength. This design suffers from at least two disadvantages. First, a sealing gasket located preferably on the lid at shelf to seal contents of a bucket would be exposed to the vertical loading attributable to bucket and any other vertically stacked buckets. This design would likely cause a gasket to rupture. Second, this design forces a user to push a closure (lid) onto a container (bucket) therefore eliminating its use as a screw-type closure.
Various inventions use a container with a single thread and a small pitch to bear a stacking load. However there are various disadvantages inherent with these structures. First, a container or closure having a small pitch necessarily has a small target area for engagably starting the closure threads on the container threads. Second, machines used for installation of screw on closures often turn closures at a rate of about 500 RPM. This speed in combination with a small target area can lead to manufacturing difficulties and stripped threads. Third, a process comprising pushing a closure onto a container, instead of screwing on a closure may lead to problems like stripped threads and uncertainty as to the orientation of closure threads relative to container threads.
In view of the deficiencies in the known container threads and closures it is apparent that a container is needed having top load seal protection characteristics as well as having a closure which is easy to install. It is also preferable that the closure be both closable and openable with a single turn.
It is an object of the present invention to provide a top load seal protection feature.
It is a further objective of this invention to provide a load bearing thread operably engaged with a container thread to divert a top load to a container.
It is still a further objective of this invention to divert a top load to a load bearing thread of a container and away from a sealing gasket located in a closure crown.
It is still an even further objective of the present invention to have the above stated characteristics and yet have a closure which is operable with a single rotation.
It is an even further objective of this invention to force the closure to move immediately upward when the cap is unscrewed and prevent cocking such that the closure and bottle maintain axial alignment in spite of the large clearance between threads.
More particularly, the present invention provides a container finish comprising an upstanding neck portion, a primary thread helically extending around the upstanding neck portion, a load bearing thread spaced below the primary thread and helically extending around the upstanding neck portion. The load bearing thread preferably starts at a point below a starting point for the primary thread and the load bearing thread is connected to the primary thread by a connecting thread portion. The connecting thread portion is preferably a horizontal thread portion extending from the primary thread. The geometry of the threads is such that the vertical distance in the target area for starting the closure is about twice the vertical distance between the primary thread and the load bearing thread.
In an alternative embodiment, the present invention provides a closure finish, comprising a top wall and a skirt depending therefrom, the skirt having a closure thread and a load bearing thread in a spaced helical relationship on an interior surface of the skirt, where the load bearing thread has a starting point or transition area above or below the closure thread at some location along the skirt and may connect to the closure thread by a connecting portion. The vertical distance in the target area of the closure threads is preferably about twice a vertical distance between said closure thread and said load bearing thread.
In yet another alternative embodiment the load bearing closure comprises a top wall having an annular skirt depending therefrom, a helically circumscribing thread along an inner surface of the skirt, at least one load bearing protuberance equidistantly spaced and integral with an inner surface of the annular skirt, and each of the at least one of the load bearing protuberances and the helically circumscribing thread forming a groove therebetween for operably receiving a container thread. There are preferably three load bearing protuberances which are preferably spaced about 120 degrees apart.